Pulse multiplex transmission system



Jh. 2, 1951 w. A. MILLER PULSE MULTIPLEX TRANSMISSION SYSTEM 3 Sheets-Sheet l Filed Jan. 4, 1947 Jan. 2, 1951 2,536,654

W. A. MILLER PULSE MULTIPLEX TRANSMISSION SYSTEM 5 Sheets-Sheet 2 Filed Jan. 4, 1947 un u ATTORNEY Jan. 2, 1951 W. A. WLLER 2,536,654

PULSE MULTIPLEX TRANSMISSION SYSTEM Filed Jan. 4, 1947 3 Sheets-Sheet 5 HZ f/LG J i n Y 11m/r -UHw-LrL---p---mw l cfm/WEL -Wml #if y /r wip m.

ATTORNEY Patented Jan. 2, 1951 WilliamA. Miller; Port Jefferson; N. Y., assignerI te Radio. Corporation of America, acci-poration of; Delaware:

Application. January 4, 19487.,` SerialNo. 720,261

(Cl: Z50-9") 12' Claims;

This invention relates toa multiplex' communication system utilizing, spaced pulses of 'electri-f cal energy, inl which the pulses corresponding to the separate channels are separatelyY and consecutively generated at atiixed repetition rate'an'd time or phase displaced. by the modulation: I'n this type of system, each cycleofoperation. inf cludes a plurality oi equal .Width (duration). channel pulses and a synchronization pulse of dii'erent (preferablyv longer) Width or duration. The pulses in each channel are time displaced by the modulation, a predetermined amount', and' the maximum displacement equivalent to 100% peak modulation is such as. to leave a. guard space between pulses from succeeding channels. This guard` space between pulses from succeeding channels is necessary to reduce crossemodulaf tion effects. The pulses fromother channels oc'- cur. in the interval between adjacent pulsesV from any one channel.

Anobject of the invention is to provide a pulse multiplex system whose output' pulses to a transmitter are of rectangular wave form and which avoids the necessity of employing limiter stages for obtaining this rectangular Wave form.

Another object is to provide a pulse multiplex transmitter system Which employs a plurality of cascade-connected self-restoring trigger circuits for each signal transmitting channel;

A further object is to provide a multiplex transfmitting systemvvhich is simple in design and. requires a small number of vacuumtube structures for each channel for producing time displaced pulses of rectangular wave form.

TheA following is a more. detailedA description of the invention, in conjunction with. a drawing, wherein:

Figs. l and' 2 illustrate.dii-ferent` transmitting circuits of the pulse multiplex communication system of the invention; and.

Fig. 3 illustrates a series of curves given in explanation ofv theY operation of the systempf the invention.

Referring to Fig, l, there. are shown a plurality of signal or intelligence transmitting channelsidentiiied as channel l, channel 2,. channel 3`, etc. to channelN, and. also the synchronizing channel for producing a synchronizing; pulse. The apparatus in channelsv I., v2, and 3,. up to channel. Nhave similar equipmentsand operate simi.- larly, except for olilierent` time. constants in cer.- tain trigger circuits of these channels. For this reason, only channels l and 2, havebeen, illustrated in detail, it being understood that channels 3, 4 etc. and channel N are similarly equipped.

Each channel is providedwithA three self-restoring trigger circuits' arranged in cascade re- Iationship. The first trigger circuit may be referred to as a channel selector, While the sec'- ond: trigger circuit' for each individualY channel may be referred to' as a modulating trigger' circuit. All oi. the lrst: or channel'selector trigger circuitsof all the channels operate simultaneously uponthe occurrence' of a synchronizing pulse pro'- duced` by the synchronizing pulse generator 2!) andappearing in the` common lead 2i in circuit with the inputs oi 'all the'channels. It should be understood', however, that the rst trigger circuits of all the signal channels, although operating.v simultaneously, have diiierent time constants.

Referring. to'. channel l, for example, the apparatus in this channel comprises a first selfrestoring trigger. circuit'A, a second self-restoring trigger circuit B, and a third self-restoring trigger circuit C; Trigger circuit A comprisesa pair oflvacuum tubes Vjand V I which, if desired', could bel included. Within a single evacuated envelope. The gridand' anode structures of trigger circuit A 'are interconnected to provide a regenerative action., The anodes oi tubes V and Vlare supplied with positive polarizing potentials fromthe positive terminalv -ioi a source of' directional po.- t'ential' through separate resistors. The anode of tube V is connected to the grid of' tube Vl through a condenser CI, While the anode oi tube Vl" is. connected to the grid of V through a resistor. The. grid ofA tube V is connected to the negativeterminal -EC' of a source of biasing po tenti'al through a. resistor T; The gridl of tube Vl is connected to. ground and to its cathode through anv adjustable resistor Rl. The cathode ofv tube Vis connected to ground through a relatively high resistor W, in turn shunted byv a diode D; rLhis diode Dis an open circuit for the nega,- tive input pulse applied. to terminal K. Such negative impulses applied tothe cathode of tube VWillcause this tubeV to conduct, and in conducting, this" tube will" draw electrons from ground, through D, shuntingv out the high resistance` W. The diode D' will dissipate all positive pulses, thus such pulses-will not affect the behavior of the trigger. The purpose'vof the diode D, is thus to provide Ia highy impedancetr-ipping circuit input without causing as much degeneration as the purely'ohmi'c resistanceW, which is ofl the order off 1% of a megohm.

In-- the-nperati-'onof trigger circuit` A, tubeV is normally. non-conductive and: biased to cut' effi by rneansrof source-EQ TubeA V iz., however, Yis nor*- mally. inra conductiveA stateand passes4 current channel I.

because its grid is maintained at or near zero bias. This condition oi operation wherein tube V is normally non-conductive and tube Vl is normally conductive is called the stable state. In the active or tripped state, however, the current passing conditions of the tubes V and VI are reversed from that just described. After an interval of time in the active state (depending in part upon the time constant of condenser Cl and resistor Rl), the trigger circuit A will restore itself to the stable state. In order to change the trigger circuit A from the stable state to the active state, it is necessary to apply a negative pulse to terminal K of suiiicient magnitude to trip the trigger circuit; that is, to reverse the current passing conditions oi the two tubes V and Vl. These negative tripping pulses are supplied over a common lead 2i from the synchronization pulse generator 25.

Trigger circuit B is similar in construction and design to trigger circuit A, except for the length of time it remains in the active state. This trigger circuit B is composed of a pair of vacuum tube triodes V2 and V3 whose grid and anode electrodes are interconnected regeneratively. It is also provided with a diode Di in the cathode circuit of tube V2. Tube V2 is normally non-conductive and tube V3 normallyT conductive in the stable state, and the current passing conditions of these two tubes are reversed in the active state. Trigger circuit B is tripped from its stable state to its active state by means oi a negative pulse obtained from the anode of tube V l via condenser C3 which couples the anode of tube Vi to the anode of diode DE. This negative pulse is to trip trigger circuit B, and occurs when the trigger circuit A restores itself to the stable state; or, stated in other words, trigger circuit B will turn on or become activated when trigger circuit A turns off or returns to its stable state. The active period of the trigger circuit B is determined by the time constant of condenser CZ and resistor R2 together with the anode resistor oi tube V2 and the direct current resistance of tube V2. En circuit with the anode of tube V2 of the trigger circuit B there is shown a triode vacuum tube V1 which is biased to operate class A on the audio input voltage supplied to its grid. Tube Vl varies the discharge rate of condenser C2 of trigger circuit B and hence varies the active time of this trigger circuit. Thus it will be seen that the tube V1 provides a discharge path for the condenser C2 which is independent of everything but the audio frequency modulating voltage. The audio input supplied to the grid of tube V? may be speech message waves or other modulation for It will thus be seen that the output of trigger circuit B is a pulse whose width or duration is modulated by the audio signal applied to this particular channel.

Trigger circuit C in channel i comprises vacuum tubes V 4, V5 and diode D2, which operates in a manner similar to trigger circuits A, B except for the time constants involved and the fact that trigger circuit C has its active period controlled by an artincial line TL. As stated before, trigger circuit C is also a self-restoring trigger circuit. It requires a negative input pulse from trigger circuit B via condenser C4 to trip it from the stable to the activ-e state. This negative input pulse to trip trigger circuit C occurs when trigger circuit B turns oi or restores itself to the stable state. Transmission line TL is an artiiicial line comprising a plurality of identical sections of series inductance and shunt capacitance. One

end of the line TL is connected to the grid of tube V5 While the other end is short-circuited, as shown. A resistor 9 is provided whose value is equal to the characteristic impedance of the line TL to insure dissipation of the puise reiiected from the short-circuited end of the line. It should be noted that the anodes and grids of tubes V4 and V5 are interconnected by parallel combinations of condensers and resistors 1 and 8. These condenser-shunt-resistor combinations assure extremely rapid current increase and current decay in the trigger circuit. When the trigger circuit C is tripped or activated by a negative pulse applied to the cathode of tube V4 from trigger circuit B, tube VB will become conductive and tube V5 non-conductive. A negative pulse Will then flow down the transmission line TL from the grid of tube V5 to the short-circuited end. At the short-circuited end of line TD5-this pulse will be reversed in polarity, as a result of which a positive polarity pulse will be sent back over line TL toward the grid of tube V5. As long as line TL remains negatively charged due to the application of a negative pulse from the anode of tube V4, tube V5 will be cut off; but just as soon as the line TL is completely discharged by the reflected pulse arriving at the sending end of the line TL, the negative bias on the grid of tube V5 disappears, as a result of which the bias -EC becomes eiective to turn tube V4 off and tube V5 on, hence ending the active period of trigger circuit C. it will thus be seen that the active period of trigger circuit C is the time the line TL remains charged. This trigger circuit is thus a line-controlled trigger circuit whose period depends upon the time delay due to the artificial line. A trigger circuit of this type is described in my copending application Serial No. 546,890, filed July 27, 1944, Patent No. 2,445,448 granted July 20, 1948, to which reference is herein made.

In circuit with the cathode of tube V5 of trigger circuit `C there is provided a vacuum tube V6 whose grid is grounded. When tube V5 conducts (during the stable state of trigger circuit C), it draws current through its cathode resistor 6 of an amount sufficient to develop a voltage across this resistor which places a positive bias on the cathode of tube V5, thus cutting off tube V5. Each time trigger circuit C becomes active, that is, turns on, tube V5 becomes non-conductive, as a result of which the bias on the cathode of tube V5 is reduced to zero and current is permitted to flow through tube V6. A pulse of voltage is then built up across resistor H in common to the outputs of all the channels. It should be noted that the outputs of all channels are interconnected by means of a common lead I5.

The delay of trigger circuit A of channel l is such that its active period ends half way between the synchronizing pulse on lead 2| and the first channel pulse, if modulation is absent. The delay time (zero modulation) of trigger circuit B is adjusted to be half as long as the delay time of trigger circuit A. The delay time of trigger circuit C, which produces a short square pulse, is controlled by the transmission line TL.

If the synchronizing pulse repetition rate is F pulses per second and there are N+1 channels, wherein N is the number of intelligence channels and 1 the synchronizing pulse producing channel, the time allotted to each channel is assente-f 5. The-delay# time offtrigger circuit A in-chanenelf2-1is adjusted so` that i-tturns' oi at1 a timer just' onef-halfi'the'timeebetween the rst andisec` ond channel pulses Cunmodula-ted). 'Trigger'cin---v cuit'B of'` channel 2 has the same delayfas triggercircuit- Bi of' channel I. Trigger circuit C-l o'fchannel 2- has the same delay astriggercir-V cuit of channelv I.

Thedelay time of the-trigger circuit- A oi."l channelI 3- (the first trigger circuit ofAthisr-cl'an-l nell is`v adjustedl so that itlvk turns oft aty atime:`

iust oneehal-i" thetime between thev second and third unmodulatedchannel pulses.l The-other triggercircuits inI channel 3` corresponding to' trigger'ci-rcuits BY and C of channel I haver-thei same" timeA delays as these respective` trigger circuits, in thev same l manner asV described above in connection with channels I andi-.-

All? ofthe rst trigger circuitsin'- the different signal-1 channels will operate at theY same time on each synchronizing input pulse but' will" have different active periods and hence turn oi at di-ierent@ times to control their respective modulator trigger circuits.

- There isalso provided asynchronizing channel in the form of aself-restoring trigger circuit comprising triode vacuum tubes 2 and 3 having incir'cuit therewith a diode ll and a transmission line TL. This trigger circuit in the synchro# nizingf channelis similar in construction and in operation to the trigger circuit C of channel I, exceptl for the fact that the time delay of the transmission linev TL is diierent from the time delay of- TL. Putting it in other Words, the ac'- tive periodi of the triggeri circuit 2, 3, 4 is different from the active period andV longer than that of the trigger circuit C. It should be noted that the synchronizing channel trigger circuit 2, 3 obtains its trippingr input pulse overv the common input lead 2l from the common synchronizing pulse -I generator 28e. In circuit with the cathode of tube V3v of the synchronizing channel is a vacuum. tube V5 Whose grid is grounded and operates in a manner similar to tube V6 ofA channel I.

The common output circuit comprises a" pulse amplier I8 and apulsed oscillatorV I9 coupled to the output lead I5 for all channels. The pulsed oscillator IS may comprise a magnetron or a Klystron; whose output is coupled tor asuitable wave.v directive structure 2 I.

AL. better understanding of the operation of the circuit of Fig. 1 may be had by'referring to the s'eriesfoi curves of Fig. 3. Curve I illustrates Whenthei negative input pulse occurs in the com- I'noniinput lead 2l. Curve 2 indicates the'outputfrom thefsynchronizing channel. Curve 3 represents' the pulses from trigger circuit Curve-4 representsthe pulses from the trigger circuit-B. Curve 5 represents the pulsesY from the trigger circuit C.

v It should benoted at this time that the'negaative synchronizing input pulse at time A starts the trigger circuits 2, 3 in the synchronizing channel' at the same timeas it starts the trigger circuit A in channel I. Trigger circuit A, as indicated in curve 3, turns off or restores itself to its stable state` at a time which is half Way between the synchronizing pulse of. curvel I and the rst channel pulse ofV curve 5, assuming no modulation'. The' double arrow on. the trailing Vedge'ot'curve II* indicatesa Width mo'dulatedpulse for-channel'A whose duration depends'upon the ino'diil'ationfor that channel. Thedouble ar'- iw'th'ough the leading and'v trailingv edges of '6T the pulse in curve- 5i indicateseartime. nrorlulateitf. pulse orfAl ai, constant` width.

Curve 611 ofi Figr; Sirepresents: the; activeatimexm output pulse for` trigger circuit A!J on' channel-25; whichv`l terminates at time Curve; -represents the active time or output pulse off' triggercircuit B-' of channel 2, while'curve 8 represents :the ac1 tivei timeor output pulse ofi trigger circuitLvCfofichannel 2f. TheA pulses-f of` curve 1 are width;E modulated-i pulses"V WhoseL durations dependL upon the modulation or audio'inputfvfor 'that particular channel; Curve 9' represents: the active'- timea on outpu-tfpulseof the' rst trigger circuitof channel 31 corresponding'to'-- the trigger` circuits- A' and:2 off channels I1 and 2. Curve lllrepresentsl. thew-idtli1 modulated pulses of'the secondl triggeric cuitfofchannel corresponding to theftrigge'rc r cuitsv Biland B- of' channelsY I and? 2i. Similar y; curve I-I1 represents the time4 modulated.. pulses: of" constant widthproduced by the=third?orrlast.v trigger circuit or channel 3S corresponding. to trigger circuits C? and C of channels` Il andi 2i.:

It-shouldbe noted from a-study of Fig; iitltiat` al1 the rst trigger circuits-otr allthe signal chan-.- nels,` and'- also the synchronizing channel, areface tivatedf or turned onati the same time by:v the negative-1 polarity synchronizing, input; pulse on. lead 2l, although all these trigger circuits' have diierentv active periods. 'l'Chus the synchronizing channelY trigger circuitV is-A turned: cnf. at. time`r andl willt turn off at tim-eB, Whiletrigger circuit A oifchannel I- which turns on-tim`e A will turn off'at timeC, and triggercircuiil Af" of channel 21l which turnsl on= attime A will turn offat'f time F; and trigger circuitV A ofy channel 3 which turns on at timeAv will turn off'at time Ii When.` trigger circuits A and A turn oft, they vrespec`V tively turn on trigger circuit'sBf andi B', andl when thesey last trigger ycircuits turn off. they in turn'will turnon trigger circuitsC" and G", ree spectively.

Theresulting output from allthe'fchannels-s shown-incurve I 2y and is-applied to thepulseeamvpliiier I8; It' should be notedthat thesync'hrovni'zing pulse in curve-l2is of longerduration than the; individual intelligenceI or signal pulse, and that these intelligence or signalpulses'ffrom` the-- different channels are of the-same Width orduration, although timedisplaced by their" associated audio# signals.

The-output from antenna 2 I isintheform ofi'a train ci: pulsesof ultra high frequencyf Waves whosedurations and spacings correspond to-the pulsesoffeurve' I2.

TheundeviatedoutputofL thecircuitof' Fig; 1 consists of a series of pulses of repetitionrate (N+1)`F, of which every (N+1) th is the synchro"- nizi-ngV` pulse, and the rst pulse after thesynchronizing pulse is from channel' I, the second pulse fromchannel 2, the third pulse from' channel 3, etc. If audio frequency voltage is'applied to the audio input of channel I, then only'the pulse-of'channel I will be deviated; likewise for channel 2, etc.

If itisdesired that there be in all ninesignal channels and one synchronizing channel; then all that is needed is a 10 kilocycle synchronizing pulse-y supplied by the synchronizing pulse generator20. The final pulse outputA from the an.- tennay 2| will be at a 100 kilocycle pulserepetition rate.

In order that high levelsv on channel I will not causethe channel I pulse to occupy atime in terval allotted to the pulse of, channel 2,. the

u anodeof vacuum tube V" of trigger circuit Nbr channel 2 is connected via lead 22 and diode D4 to the grid of tube V3 of trigger circuit B of channel I. Thus, when trigger circuit A' of channel 2 .restores itself to the stable state (turns oi), a positive pulse is applied to the grid of tube V3 of trigger circuit B. If trigger circuit B is in the stable state (in which tube V3 is already conducting), nothing will happen, but if trigger circuit. B has not yet restored itself, the positive pulse on lead 22 will restore trigger circuit B to its stable state and cause tube V3 to conduct, thus turning oi channel I. The 'negative pulses on lead 22, which occur when trigger circuit A of channel 2 turns on, are by-passed to ground by diode D3. The resistor29 in series with the anode of diode D3 is important in the operation of the system because when the trigger circuit B is changed from the stable state to the active state there must be a negative going pulse present on the grid of V3. This would be hard, if not impossible to accomplish, if this resistor were not present since D4 and D3 would be a low impedance to ground if the anode of D3 were directly connected to ground. The resistor 2S must be small enough to allow the condenser in the line 22 to discharge in the intra-channel time but not small enough to hamper the triggering action of B.

If all the channels are interconnected in this manner, no channel interference will occur due to greater than 100% modulation. Stated otherwise, the inter-connection between the channels prevents cross modulation and assures a guard space between theoutput pulses from succeeding channels. As an illustration only, each channel pulse may occur at a rate of 10 kilocycles and the separation between adjacent pulses in each channel for an unmodulated condition may be 100 microseconds. Hence, the channel pulses may be spaced l microseconds apart in the common output circuit. The pulses in each channel can be modulated plus and minus 31/2 microseconds (peak modulation), thus having a guard space between pulses from succeeding channels of about *3 microseconds. The radio frequency output from the pulse oscillator l?) may be of the order of Go megacycles or higher.

Fig. 2 illustrates another and a preferred embodiment of a pulse multiplex transmitting system which has the advantage over Fig. 1 of requiring fewer tubes for the equipment of each channel. Here again, as in Fig. l, trigger circuits are employed as modulators, but the outputs from the various intelligence channels are coupled in common to a channel pulse generator.

Referring to Fig. 2 in more detail, there is shown a constant frequency oscillator Sil, for example, a crytsal controlled oscillator, which is carefully adjusted to produce a constant irequency (N4-DF, whorein N is the number of intelligence carrying channels and El is the synchronizing pulse repetition rate, as described above in connection with Fig. l. The output of oscillator 3U designated by waveform M is coupled to a vacuum pentode threshold and peak limiter 3l which serves to generate square topped (and bottomed) waves from the sine wave oscillations 'supplied thereto. This output designated by waveform N is fed to a c unter circuit 32 which includes a condenser 43, a pair of diodes 42 and i5 (which may be arranged within a single evacuated envelope or comprise two separate tubes, as

shown), a condenser dii, a normally non-conductive triode vacuum tube 4l, and a pulse tra-nsormer 46. This counter may be called a stepwave generator since its output (which is supplied va lead 4l to the grids of cathode follower tubes 33 and 35) is in the form of a series of steps or stairs corresponding to the incremental voltage increases counted by the counter. Condenser 43 is of much smaller value than condenser Li and may have a ratio, for example, of any- Where in the range of l to l5 to l to 20. Tube 41 and transformer i6 in the counter circuit may be considered as a one-shot pulse oscillator Which passes a voltage pulse when the voltage stored on the condenser i4 reaches a critical value suicient to overcome the cut-on` bias on the tube 4l. The bias resistor R in the cathode circuit of tube 41 is adjusted so that tube lll is non-conductive until the grid voltage stored on the condenser 44 reaches a value corresponding to N-l-l impulses supplied thereto by the oscillator 30.

In the operation of the counter circuit, diode t2 will not conduct for the positive r.'sing edge of a pulse from the limiter 3i but diode 45 Will conduct; and hence the circuit will appear as though the two condensers 43 and 4d are in series to ground. Hence, for example, one-twentieth of the total input voltage appears across condenser id (for the foregoing assumption that condenser 1&3 has a size which is one-twentieth that of condenser 4t). On the negative falling edge of the pulses from the limiter 3l, diode 42 will conduct but diode te' will not conduct, leaving unchanged the voltage on condenser 44 acquired during the immediately preceding rise of the pulse. The voltage on condenser 63 will be completely discharged through diode 42 during the negative drop. During the next positive rise of the pulse applied to the counter by the limiter, the condenser will recharge through diode 45. Each time there is a positive rise in voltage applied by the limiter 3! to the condenser 43, there will be an incremental increase or step-up in voltage on condenser lili, aithough the charge on condenser for each increase is slightly less than the preceding one. It should be noted that there is no resistance established across condenser 44 because it is desired that there be complete absence oi `current or charge leakage on this condenser during the voltage step-up operation.

The step-up of the charge on condenser 44 at the end ci a desired rise (the ninth rise if nine channels are employed) will cause vacuum tube ill to start conducting very suddenly, as a result or" which a pulse of current is passed through transformer S- which is so'poled that it applies a very sharp positive pulse to the grid of tube 41, thus expediting or hastening the now of current from the tube d?. Stated otherwise, tube 41 and transformer t@ are, in effect, an over-biased pulse oscillator which is connected regeneratively to produce only one pulse in response to the application of a voltage stored on condenser 44 which reaches or exceeds the critical value of the tube 4l. When tube 4l conducts, it produces a low impedance path for the charge on condenser 44. This condenser is then discharges through tube 4l to a relatively low value. The counter 32 can be arranged to provide a different number of steps or rises in the wave output therefrom by varying the ratio of the capacitance value of condenser 4-3 and di?, if a different number of channels are employed.

The tubes 33 and 34 are merely cathode followers which derive a step voltage wave input from the counter circuit over lead 4I. These cathode followers or coupling amplifiers provide an output from their respective cathodes of the of channel 2 is in the active state.

tube to conduct. When tube t9 conducts, there is a voltage drop in resistor 31 which causes the application of a negative tripping pulse to the channel pulse generator 1I, 12. It should be noted that resistor 31 is in common with outputs of all the triode tubes 59, 69' etc. of the different signal channels, and that the channel pulse generator 1l, 12 is also lin common with outputs of the signal channels.

The channel pulse generator 1l, 12 is of the self-restoring type and has its active period controlled by an artificial line TL. It operates in a manner similar to the synchronizing pulse generator, except for the duration of the active period which., in turn, is controlled hv the time constant of the articial line. The channel pulse generator 1l, 12 produces a pulse of eX- tremelv short duration. and this pulse appearing on the cathode of tube 12 is applied to the cathode of triode 11. Triode 11 has its grid connected to ground and is normallv nonconductive. When the channel pulse generator is activated or tripped. the tube 11 conducts for vthe duration of the active period of the channel pulse generator. y

It should. be noted that the output from the synchronizing pulse generator 55. B is also derived from the cathode of tube 5G which is connected to the cathode or triode 555. 'Friede 65 is normally non-conductive and operates to nass a pulse of current for the duration of the active period of the synchronizing pulse generator; It should be noted that the anode nf the tube 5S is connected to the anode ni' tube 11 and that both anodes are connected via lead 80 to a common pulse ampliiier and radio frenuency oscillator,

' not shown. Thus the channel pulses are combined With. the synchronizing pulses.

Channel 2 operates in substantially the same manner described above in connection with channel I. When selector Eil' is turned on (made to conduct), a negative pulse is passed on to the pulse modulator 61', Sii and trips this modulator. When this pulse width modulator 51', 68 returns to its stable state, the output of 69' causes the channel pulse generator 1l, 12 to produce a channel pulse for channel 2.

In order that over modulation of channel l will not produce interference in channel 2, the positive pulse generated at the beginning oi operation of channel 2 at the anode of tube 68' is fed via lead 18 and diode 19 to the grid of tube 68 of channel i in order to assure the fact that the pulse width modulator of channel l is restored or returned to its normal stable state. This prevents interference and makes it impossible for the pulse width modulator trigger circuit 61, 68 of channel i to be 4in the active state during the time pulse Width modulator 61', 68 Similar cross connections are employed between channels 2 and 3, and channels 'l and 5, etc. Substantially the same feature has been described above in connection with Fig. 1, to prevent cross modulation of the channels.

The resultant output of the transmitting system of Fig. 2 is similar to the showing curve I2 of Fig. 3.

An important advantage of the present invention is that I am able to obtain a square wave output for the pulse amplifier and radio frequencyl oscillator Without the necessity of utilizing limiting stages in the output of the system.

What is claimed is:

1. A transmitting terminal station for a pulse? multiplex communication system wherein a common transmission medium is sequentially assigned to a plurality of channels on a time division basis, comprising synchronizing channel apparatus having a self-restoring trigger circuit. a plurality of signal channel circuits each including a self-restoring regenerative trigger circuit and a signal modulating circuit coupled to said trigger circuit for varying the active time thereof in dependence upon the modulation, whereby the output from said trigger circuit is a width modulated pulse. a source of tripping pulses in common to the input elements of all said signal channel circuits and said synchronizing channel, means for converting the width modulated pulses in said signal channel circuits to time displaced constant duration pulses, and a common output circuit for all channel equipment, said common output circuit including a radio frequency oscillator and a Wave directive structure coupled to said oscillator.

2. A transmitting terminal for a pulse multiplex communication system wherein a common transmission medium is sequentially assigned to a plurality of channels on a time division basis, comprising a synchronizing pulse producing circuit in the form of a self-restoring trigger circuit, a plurality of signal channel circuits each. including a pulse width modulator in the form of a self-restoring regenerative trigger circuit having a signal modulating circuit coupled thereto to vary the active time thereof, a source of pulses connected in common to all of said trigger circuits for activating the samel means for converting the Width modulated pulses in said signal channel circuits to time displaced constant duration pulses, and a common output circuit for said signal channel circuits and for said synchronizing pulse producing circuit, said common output circuit including a radio frequency oscillator and a wave directive structure coupled to said oscillator.

3. A transmitting terminal station for a pulse multiplex communication system wherein a common transmission medium is sequentially assigned to a plurality of channels on a time division basis, comprising synchronizing channel apparatus having a self-restoring trigger circuit. a pluraliti7 of signal channel circuits each including a self-restoring regenerative trigger circuit and a signal modulating circuit coupled thereto for varying the active time thereof in dependence upon the modulation. a source of tripping pulses in common to the input elements of all said signal channel circuits and said synchronizing channel, the time constants of said trigger circuits in said signal channels being different, whereby said trigger circuits have diierent active periods and produce width modulated pulses. means for converting the Width modulated pulses in said signal channel circuits to time displaced constant duration pulses, and a common output circuit for said synchronizing apparatus and for said signal channel circuits, said common output circuit including a radio frequency oscillator.

4. A transmitting terminal for a pulse multiplex communication system comprising a source of constant frequency oscillations, means for producing impulses from said oscillations, a counter circuit coupled to said means and producing a cyclically recurrent step wave voltage, each cycle of which has as many steps as the nurnber of signal channel circuits, a pair of coupling ampliiiers individually coupled t0 the output of said ountgr circuit and each passing said step Wave one degree of electrical stability and which becomes activated at the end of the recurrent step wave voltage cycle, a channel pulse generator comprising a self-restoring trigger circuit having only one degree of electrical stability coupled inparallel to the outputs of said signal channel circuits, said channel pulse generator being responsive to the restoration of the trigger moduiator circuits in the different channel circuits for producing time displaced co-nstant duration pulses, means for combining the outputs of said channel pulse generator and said synchronizing pulse generator, and means interconnecting the trigger circuit modulator of any one channel with the trigger circuit modulator of a preceding channel for assuring the restoration of the last trigger circuit modulator When the succeeding trigger circuit modulator is activated.

9. A transmitting terminal station for a pulse multiplex communication system wherein a common transmission medium is sequentially assigned toa plurality of channel circuits on a time division basis, comprising a plurality of signal channel circuits each including first, second and third cascade connected self-storing trigger circuits, a signal modulating circuit for varying the active time of the second trigger circuit in each channel circuit in dependence upon the modulation, whereby the output from the second trigger circuit is a width modulated pulse, a connection between the rst and second trigger circuits in each channel circuit for tripping the second trigger circuit upon the restoration of the iirst trigger circuit, a connection between the second and third trigger circuits in each channel circuit for tripping the third trigger circuit upon the restoration of the second trigger circuit, said third trigger circuits pro ducing constant duration pulses, said rst trigger circuits having different time constants of such values that upon simultaneous tripping they restore themselves at different times, a source O'i recurrent tripping pulses in common to the inputs of all of said first trigger circuits, the active period of each first trigger circuit ending at a time subsequent to the termination of the tripping pulse therefor and before the operation of its associated third trigger circuit in the same channel circuit, and a common output circuit coupled to all of said third trigger circuits, said common output including a radio frequency oscillator.

10. A transmitting terminal station for a pulse multiplex communication system wherein a common transmission medium is sequentially assigned to a plurality oi channel circuits on a time division basis, comprising synchronizing channel apparatus having a self-restoring trigger circuit, a plurality of channel circuits each including rst, second and third cascade connected self-restoring trigger circuits, a signal modulating circuit for varying the active time of the second trigger circuit in each channel circuit in dependence upon the modulation, whereby the output from the second trigger circuit is a width modulated pulse, a connection between the first and second trigger circuits in each channel cir- 1 circuits having different time constants of such values that upon simultaneous tripping they restore themselves at dinerent times, a source of recurrent tripping pulses in common to the inputs of al1 of said first trigger circuits and said synchronizing channel apparatus, the active period of each rst trigger circuit ending at a time subsequent to the termination of the tripping pulse therefor and before the operation of its associated third trigger circuit in the same channel circuit, and a common output circuit coupled to all of said third trigger circuits and to said synchronizing channel apparatus, said common output including a radio frequency oscillator.

11. A transmitting station in accordance with claim 10 characterized in this, that the self-restoring trigger circuit of the synchronizing channel apparatus has an active period shorter than the active periods of any of the first trigger circuits of the channel circuits.

12. A transmitting terminal station for a pulse multiplex communication system wherein a common transmission medium is sequentially assigned to a plurality of channel circuits on a time division basis, comprising synchronizing channel apparatus having a self-restoring trigger circuit, a plurality of channel circuits each including a self-restoring trigger circuit and a signal modulating circuit coupled to said last trigger circuit for varying the active time thereof in dependence upon the modulation whereby the output from each modulated trigger circuit is a width modulated pulse, a source of tripping pulses in common to the inputs of all signal channel circuits and said synchronizing channel apparatus, means in the diierent channel circuits and coupled to the inputs of their associated trigger circuits and responsive to the tripping pulses from said source for operating the trigger circuit in the dilerent channel circuits at different non-overlapping times, said trigger circuit in the synchronizing channel apparatus having such time constants that its active period ends before the operation of the trigger circuits in the signal channel circuits, and self-restoring trigger circuit equipment coupled to the modulated trigger circuits in said signal channel circuits and responsive to the width modulated pulses produced in said channel circuits for producing time displaced pulses of constant duration.

WILLIAM A. MILLER.

REFERENCES CITED The following references are of record in the file of this patent:

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